Parasites of mollusks are studied to determine: their identity, molluscan host range, mode of transmission, localization and pathology of infection, relation to schistosome infections, and potential use for biological control. Selection and crossing experiments are conducted to find additional genetic markers in Biomphalaria glabrata and B. straminea, to increase knowledge of molluscan susceptibility to infection with Schistosoma mansoni and assess the potential for genetic control. Selection and crossing experiments are conducted with S. mansoni to analyze the genetic variation in snail infectivity in different strains of the parasite, to better understand the epidemiology of Schistosomiasis. Abnormal tissue growths observed in the course of the above investigations are studied to determine their cause; genetic, infection or other. Hemopoiesis and genetic tendencies for formation of aggregations of amebocytes are being studied.